In this work, a green and clean tanning technology based on the polyhedral oligomeric silsesquioxane sodium carboxylate(POSS-COONa) and zirconium sulfate was studied to relieve the environmental pressure and resource strain caused by chrome tanning. Firstly, amino sesquisiloxane was prepared from γ-aminopropyl triethoxy silane by hydrolysis and condensation method, and then was substituted with sodium chloroacetate to form POSS-COONa. The POSS-COONa had crystallinity and maintained cube structure by X-ray Diffraction and Transmission Electron Microscopy. The POSS-COONa and zirconium sulfate were applied in chrome-free tanning process of goat skin. Compared with zirconium sulfate tanned leather, the shrinkage temperature of combined tanned leather increased from 83.5 ℃ to 90.5 ℃, the thickening rate increased from 88% to 118.3%, and the softness increased from 5.9mm to 6.5mm. The Scanning Electron Microscopy and Energy Dispersive Spectroscopy showed that combined tanned leather fibers were braided loosely, and POSS-COONa and zirconium sulfate could be evenly dispersed among the collagen fibers. The tensile strength, tear strength and elongation at break of the combined tanned leather with POSS-COONa and zirconium sulfate were 26.4 N/mm2, 96.3 N/mm and 105.5%, which were similar to those of the tanned leather with zirconium sulfate. Based on the above results, POSS-COONa and zirconium sulfate tanning has a promising future in clean production.
The conventional beamhouse of leather manufacturing invariably results in pollution of ammonia-nitrogen (NH3-N), chloride and chromium in wastewater, which is seriously restricted the sustainable development of the leather industry. In order to minimize the emissions of harmful chemicals, an integrated non-ammonia bating, salt-free pickling and high exhaustion chrome-tanning technology was designed and optimized. The results indicated that, being superior to the conventional bating-chrome tanning process, the novel technology almost eliminates the NH3-N and chloride pollution by using salt-free pickling auxiliaries and acidic proteases. In the novel technology, the total Cr utilization ratio was increased to 94.9% from 80.4%, the residual Cr concentration in the tanning liquor dropped to 294 mg/l from 1134 mg/l. Additionally, total residual contents of total nitrogen (TN), total organic carbon (TOC) and chemical oxygen demand (CODCr) were reduced by 75.7%, 37.1% and 45.2%, respectively. The scale-up experiments were conducted in furniture and shoe upper leather factories verified that the novel method was acceptable in the aspects of physical and organoleptic properties of the resultant leather. It is anticipated that the effluent liquors containing very small amounts of NH3-N, chloride and chromium can be more easily disposed. The established novel technology can be evolved as an environment-friendly technology and matches the integral requirements of the modern sustainable leather industry.
Tanning is an essential process for the production of leather using mineral and vegetable tanning agents. Tanning stabilizes proteins of raw hides/skins and determines the ultimate quality of the finished leather. The intense pressure of the chrome-containing solid and liquid wastes of tanneries urges the leather industries to seek alternative tanning agents due to their environmental restrictions. In this study, an attempt was taken to apply novel vegetable tanning agents in leather processing extracted from Xylocarpus granatum bark. A comparative study was conducted with conventional vegetable-tanned leather tanned with mimosa and quebracho tannin. The leather tanned by Xylocarpus granatum bark extract showed the shrinkage temperature (Ts) 86.34±1.52 ˚C, and the physicomechanical properties such as tensile strength 298 kg/cm2, tear strength 39 kg/cm, grain cracking load 29.33 kg, distention at grain crack 14.50 mm, ball bursting load 40.33 kg, and distention at ball bursting 16.58 mm that was quite comparable and superior to the conventional vegetable-tanned leather and the standard recommended by United Nations Industrial Development Organization (UNIDO). The fibre structure of the experimental leather was observed through Field Emission Scanning Electron Microscopy (FE-SEM) and found tighter than that of conventional vegetable-tanned leather. Thus, Xylocarpus granatum bark extract can be a good alternative to mimosa or quebracho as a prospective vegetable tanning agent in leather processing.
The global context of climate change and the events related to the origin of the COVID-19 pandemic call for a paradigm shift in industrial process technologies. Enzymatic unhairing is presented as a sustainable alternative: not only reduces the emissions of hydrogen sulfide, but its biotechnology obtaining is friendly to the environment. However, their characterization through their enzymatic activity and histological action is necessary. Fungal enzymatic extract (EE) was obtained in a batch liquid medium using substrate from hairsaving unhairing process. Keratinolytic activity (quantitative test) was 2.7 U ker and protein 0.6 µg / ml. EE was tested at laboratory scale on submerged bovine skin with biocide 0.2% w/w, anionic 0.1%, non-ionic 0.5% tensioactives in soaking and unhairing, incubated at 37°C in shaking. Different conditions of EE were tested: dilutions (1:1, 1:2, 1:4) with buffer Tris-HCl 0.1 M, pH 9 and incubation times (24 h and 48 h). Controls were tested in the same conditions without EE. Samples of skin were observed by SEM. According to the morphological changes, score was defined to the following parameters: hair, epidermis with normal patterns; detachment of hair follicle sheath; absence of epidermis; empty hair folliclesvisible dermal papilla. Results have shown the highest values with EE 1:1, 48 h and 24 h. In 1: 4, 24 h and 48 h, the average values were lower, control samples were close to zero. In conclusion, the observations have shown a linear correlation between the EE conditions and its action on the skin.